Triclinic mesotartaric acid monohydrate crystallizes in P I with Z= 2 and a = 5.516, b = 9.220, c = 7.330/~ and ct= 115.11, p= 93.62, r=93.64°; the monoclinic monohydrate in P21/c with Z=4 and a= 5.215, b=5-019, c=25-92/~ and/~=99.72°;the triclinic anhydrous modification in PI with Z=2 and a= 9-459, b = 6"464, c = 5"396/~ and ct = 68.99,fl= 76.36, r = 75.77°; and the orthorhombic anhydrous modification in Pbn21 or Pbnm with Z= 16 and a= 19.05, b= 9.88, c= 12.16 A. The first three structures were solved by application of the correlation method to projections and refined by three-dimensional least squares.The molecules are not centrosymmetric but have the staggered conformations as found earlier in mesotartrates.In the monoclinic modification the carbonyl group in one of the planar halves of the molecule is, surprisingly, not at the side of the ~-hydroxyl group.The other intramolecular bond lengths and angles are approximately the same for the three structures.In the networks of hydrogen bonds, carboxylic acid dimers and hydrated links are of primary importance.
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Bootsma et al. (1967) studied this question.